This application claims the priority of German Patent Application No. 198 27 420.3, filed Jun. 20, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for operating an NOx trap for an internal combustion engine.
DE 196 53 756 discloses a control device for operating an NOx trap for an internal combustion engine. The control device determines the metering of a regenerating agent on the basis of individual working cycles of the engine.
It is a goal of the present invention to provide a method for operating an NOx trap for an internal combustion engine with metering of the regenerating agent. For this purpose, provision is made (1) for determining the number of working cycles required for regeneration of the NOx trap, which corresponds to metering of fuel as the regenerating medium; and (2) for taking into account additional parameters that influence the delay between the metering of the regenerating medium and its becoming effective in regenerating the NOx trap. Thus, consideration is given to the fact that the fuel initially supplied for regeneration is not in fact available for regeneration of the NOx trap, but instead forms a fuel film on a wall in an intake channel to the engine and breaks down the oxygen that is bonded in catalytic converters upstream of the NOx trap and possibly in the NOx trap itself.
The present invention takes these parameters into account (e.g., fuel film on a wall, quantity of bonded oxygen) in determining the number of working cycles required for regeneration of the NOx trap. Alternatively, it is possible to feed fuel into the combustion chamber by direct fuel injection using the control device according to the present invention, thereby not forming a fuel film on an intake wall. Alternatively or in addition, a catalytic converter can be located upstream of the NOx trap when using the control device according to the present invention. The quantity of oxygen that can be stored in the catalytic converter is minimized. In the most favorable case, the catalytic converter has no ability to store oxygen. The present invention can be used for both diesel and gasoline engines.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.